Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$37.58	7.675%	$40.4643	$40.46	$40.45	$40.50
Purchase #2	$242.63	12.795%	$273.6745	$273.67	$273.65	$273.70
Purchase #3	$149.28	13.115%	$168.8581	$168.86	$168.85	$168.90
Purchase #4	$70.90	7.365%	$76.1218	$76.12	$76.10	$76.10
Purchase #5	$98.58	10.200%	$108.6352	$108.64	$108.65	$108.60
Purchase #6	$64.27	13.504%	$72.949	$72.95	$72.95	$72.90
Purchase #7	$65.62	3.429%	$67.8701	$67.87	$67.85	$67.90
7 purchase totals =	$728.86		$808.5730	$808.57	$808.50	$808.60